Andromeda went on sale pretty soon after release and currently goes down to about $20-30 USD. Here are some threads discussing this topic, but most users will say that the game is worth getting at the discounted price.

Do I need to play the OT before playing Andromeda?

Technically, no. However, it is generally highly recommended you do so, as playing the OT will greatly enhance your understanding of MEA.

People speculate that the Asari mercenary Wrex was friends with, and later fought with, was Aria. When Wrex tells you this story in ME1, he gives her the name Aleena, but since obviously Aria is a fake name anyway to keep her safe on Omega, it's still possible.